This invention relates generally to a monolithic solar battery, and particularly to an improved monolithic solar battery including a plurality of P-N junction unit solar cells mounted on a substrate. Recently, solar batteries have been used as a power source for operating small electronic devices, such as electronic wristwatches and pocket calculators. These P-N junction solar batteries include a semiconductive substrate material, such as silicon or gallium arsenide. The voltage obtainable from these solar batteries is dependent upon the size of the band gap energy of the semiconductive material. For example, a silicon solar battery provides about 0.5 volts and a gallium arsenide solar battery provides about 0.9 volts.
An electronic wristwatch requires a voltage drop of about 2 volts and a portable electronic calculator requires about 4 volts for operation. Thus, when these solar batteries are used as power sources for such electronic devices, a plurality of solar batteries of this type must be connected in series. Conventionally, the connection was accomplished by methods such as wire bonding, face-down bonding, tape carrier, and the like. However, each of these methods has serious deficiencies, inasmuch as they involve complicated mountings, high cost of assembly and low reliability of the products. Accordingly, now that solar battery technology has improved and the batteries may be mass produced, it is desirable to provide an improved monolithic solar battery comprising a plurality of unit solar cells mounted on a substrate for use in small electronic devices, such as electronic wristwatches and portable electronic calculators.